(1) Field of the Invention
The present invention relates to a method for treating an organohalogen compound, particularly, to a preferred method for treating the organohalogen compound by destructing the organohalogen compound with a catalyst.
(2) Description of the Prior Art
Organohalogen compounds contaminate air, rivers, water underground, soil, etc. Particularly, the organohalogen compounds having toxicity such as a cancer-causing property are regarded as problems in view of environmental pollution. Release suppression technology of the organohalogen compound, and destruction-treatment technology of the organohalogen compound existing in the environment as contaminants after releasing are now under development. The above destruction-treatment technology is aimed at destructing the organohalogen compound in released waste or in the environment after releasing. Therefore, an object of the destruction-treatment is the organohalogen compound of relatively low concentration. Currently, there are some organohalogen compounds which are regarded as a source material of ozone layer destruction, or a source material of green effect, even if it may be less toxic. Therefore, release suppression technology and recovery-treatment technology for such organohalogen compounds are now under development. In the recovery-treatment technology, a large amount of recovered organohalogen compound is treated for destruction. Therefore, in view of economical aspect of the facility, it is necessary to destruct the organohalogen compound of relatively high concentration, and to make it harmless.
As for a treating method to make the organohalogen compound harmless, there are various methods which are well known. Among the various methods, a method for destruction by combustion, a method for destruction using plasma, and a method for destruction by cracking using high temperature steam have a large defect such as a large energy consumption. A method for destruction by ultraviolet ray, a method for destruction by irradiation, and a method for destruction using a micro-organism have a small destruction efficiency and a small destructing velocity. A method for destruction of an organohalogen compound using combustion has a problem to generate strong poisonous substance such as dioxine. On the contrary, a method for destructing the organohalogen compound using a catalyst receives an attention as a most effective method, because the method scarcely has the above described defects.
As for the method for treating organohalogen compounds using a catalyst, various methods have been disclosed hitherto, for example, as follows; JP-A-52-114468 (1977) disclosed a treating method using a catalytic destruction apparatus of air including an organohalogen compound. JP-A-3-42015 (1991) disclosed a method for destructing recovered flons. JP-A-3-66388 (1991) disclosed a treating method of flon of high concentration such as 6 mole %.
Destructing objects of the treating method disclosed in JP-A-52-114468 (1977) are organohalogen compounds of extremely low concentration. Therefore, it is difficult to destruct recovered organohalogen compounds, of which treatment has currently been becoming necessary, with a high efficiency under a high concentration. The treating method disclosed in JP-A-52-114468 (1977) does not teach any countermeasure against corrosion products, which are generated with heating the organohalogen compound, because concentrations of corrosive materials (chlorine, hydrogen chloride, fluorine, hydrogen fluoride etc.) generated at the destruction of the organohalogen compound are low. Furthermore, the treating method taught only insufficient countermeasure against corrosive materials generated with destructing the organohalogen compound. The method disclosed in JP-A-3-42015 (1991) is a method treating organohalogen compound of low concentrations such as 5000 ppm, and therefore, no countermeasure for the corrosive materials generated at heating and destructing the organohalogen compound was taught, which is the same as JP-A-52-114468 (1977).
The treating method disclosed in JP-A-3-66388 (1991) did not teach any practical means for supplying flon of a high concentration, nor any countermeasure against corrosive materials generated by heating the organohalogen compound. Furthermore, no practical countermeasure against corrosive materials generated at destructing flon was taught except neutralization with an alkali.
One of a few defects of the destruction method for an organohalogen compound using a catalyst is a smaller destructing efficiency than destructing efficiencies of the destructing method by combustion and the destructing method by plasma. The destructing efficiencies of the organohalogen compound by the destructing method by combustion and the destructing method by plasma is approximately in a range of 99.999.about.99.9999%. On the contrary, the destructing efficiencies of the organohalogen compound by the destructing method using a catalyst is approximately in a range of 99.9.about.99.99%. The above destructing efficiencies of the destructing method using a catalyst scarcely make a problem in practical use. However, when the method is applied to a material such as flon, to which the United Nation Environmental Plan gives a guideline for the destructing efficiency as at least 99.99%, it is necessary to add an extra means in order to comply with the guideline. For example, JP-A-6-106172 discloses a method, in which undestructed organohalogen compound in exhaust gas from the catalytic destruction process are eliminated from the exhaust gas by being adsorbed into an adsorbent. The undestructed organohalogen compounds adsorbed in the adsorbent are released and treated again with the catalyst. However, in accordance with the above method, the main catalytic destruction process must be stopped when the released undestructed organohalogen compounds from the adsorbent are treated, and accordingly, the operation efficiency of the catalytic destruction facility is decreased.
As explained above, conventional methods for treating the organohalogen compounds have difficulty in operating the facility for destructing the organohalogen compound of a high concentration with a high destructing efficiency, a high operating efficiency of the facility, and appropriate countermeasures against corrosive materials generated by the destruction.